Is there any performance different between hosting your asp.net in mono on linux and iis on window server?
In regards to the suggestion by lextm that publishing the results of perf comparisons is "not possible", the End-User License Agreement (aka EULA) for Windows Vista Ultimate allows it, with conditions.
MICROSOFT .NET BENCHMARK TESTING. The software includes one or more components of the .NET Framework 3.0 (“.NET Components”). You may conduct internal benchmark testing of those components. You may disclose the results of any benchmark test of those components, provided that you comply with the conditions set forth at http://go.microsoft.com/fwlink/?LinkID=66406. Notwithstanding any other agreement you may have with Microsoft, if you disclose such benchmark test results, Microsoft shall have the right to disclose the results of benchmark tests it conducts of your products that compete with the applicable .NET Component, provided it complies with the same conditions set forth at http://go.microsoft.com/fwlink/?LinkID=66406.
The conditions, as I read them, are reasonable disclosure requirements: the source code you used to do the testing, the versions of software you tested, the date you conducted the tests, the configuration and optimizations you made, etc.
The EULA for Windows Server 2003 includes the same provisions. I couldn't find the EULA for Windows Server 2008 (the latest incarnation) but I assume the benchmarking provisions remain.
Addendum: If you look in the EULA for Windows7, you will probably find a no-benchmarking clause, or more accurately a no-publish clause; this is because Win7 is still in pre-release. When it is officially released, expect the standard benchmark publishing conditions to be present.
In the past Microsoft had a more restrictive policy on this topic. Basically: you need permission from us (Microsoft) to disclose performance comparisons. This policy has been relaxed, even retroactively to .NET v1.0 and v1.1, as per the link in the above EULA.